


Heart Boner

by Tea_Cup (PumpkinFlash)



Category: Underfell - Fandom, Undertale
Genre: F/M, My First Smut, Smut
Language: English
Status: Completed
Published: 2019-08-20
Updated: 2020-07-15
Packaged: 2020-09-18 21:15:49
Rating: Mature
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 2
Words: 4,476
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/20319619
Author URL: https://archiveofourown.org/users/PumpkinFlash/pseuds/Tea_Cup
Summary: You go on a “girl’s night out” with your friends and things don’t go as plan. But then again, when do they ever?





	1. Serenade

Note:

If you haven’t heard the song before either listen to it before you read or after. But please don’t read it during the actual singing parts because the story doesn’t align with the song. If you haven’t heard the song before I personally recommend listening to it afterwards to help avoid spoilers.

[(Heart Boner by Ninja Sex Party)](https://www.youtube.com/watch?v=TS_OWTKCUIM)

* * *

It’s late at night as you get ready to meet your friends. Checking yourself in the mirror; you’re wearing a grey hoodie dress, with laced thigh high socks held up by a garter belt, and heels. Hearing a honk, you grab your phone, wallet, and keys before heading out the door. Locking it up you enter your friend’s car through the passenger door.

“Hey.” Emma greets, giggling at your outfit. 

“What got a problem with my outfit.” You question.

“You know that’s not what they meant when they said dress for da club.” She says with a chuckle.

“Yeah, well I don’t have any stripper clothes and they know the bar ain’t exactly my scene.”

“You say that but then you end up having fun anyway.” She starts the car and begins heading towards a recently popular bar, Grillby’s.

“I think it’s more I just end up entertaining you is all.” 

After listening to a couple of song and some friendly banter, the two of you are pulling into the parking lot of Grillby’s. Successfully entering the bar. “You should be happy they don’t have a dress code.” Emma teases.

“Please, there isn’t a place on the earth that can keep me out.” Looking around the club, it’s a lot bigger on the inside. In the center of the room is a dance floor full of dancing monsters and a few humans. On the left is a small stage and along the walls are a few tables and booths. At the back of the room is the bar. Both of you release a tired sigh, at the thought of having to cross the dance floor. Glancing at each other you give a fist bump of good look before navigating the dance floor.

Emma chooses to dance her way through the crowd while you walk through. Occasionally side steeping, hopping over, and ducking under the other patrons. It isn’t long until you both reach the bar, where your friends are already drunk.

“Did we miss the party?” You ask the two girls barely able to sit in their chairs. Ya know it was probably a bad idea for the two designated drivers to come in the same car. 

“Trrriiiiiiicks” Sami drunkenly yells. She tries to hug you but it’s more like she’s draping herself on you.

“Hey! Why ain’t yo sexy!?” Ami asks. Placing Sami on her stool, you try to make sure she’s balanced.

Emma nudges you in your side “Pst, she’s talking to you.”

Chocking on your laugh, you slap Emma before addressing Ami, “Sup Aims?”

“Yo! How yo gonna be my wing a man if ya a gram!” She yells slamming her shot glass on the bar.

Shoulder quacking with laughter, you point to some discarded chicken wings on the counter. “Don’t know guess you’ll have ta  _ wing _ it.” A surprised snort comes from Emma and the ironically bulky skeleton monster beside you.

“Noooooooo, shut up.” Sami whines.

“What too  _ hot _ to handle?” You ask just as a fire elemental walks by, earning more laughter from those around you.

“Dats it Om outta ‘ere!”

“Looks like someone’s funny bone is broken.” Sami tries to cover your mouth but ends up swiping the air in front of you.

“Are you going tell puns all night?” Emma asks already knowing the answer.

“ _ Tibia _ honest, I’m not sure.”

“No! No puns! I’m gonna dance.” Sami shouts, getting up from her stool along with Ami and heading to the dance floor.

“You mean wiggle?” Emma tease as the two of you take their seats. Sami turns around and sticks her tongue out before heading off to the dance floor.

“Man, I need to have what they havin’.” You comment with a playful smirk.

“Oh please.”

Waving down the bartender you order a chocolate shake while Emma orders a Bloody Mary. The bartender gives you an unimpressed look.

“Hey if ya didn’t want peeps to order it, ya shouldn’t have put it on the menu.” You tease with a waggle of your eyebrow.

Snickering, “she’s right, grillby.” The skeleton agrees with a tilt of his shot glass.

“See he gets it, ain’t no  _ bones _ about it.” You point your thumb in his direction. Grillby rolls his eyes before leaving to prepare your drinks. Turning to the skeleton you extend your hand, “Hey, ma friends call me Tricks, nice ta meet ya.”

The skeleton grabs your wrist, removing the joy buzzer from your hand. “heh, the name’s sans, sans the skeleton.” Sans has red eyelights with sharp teeth, one replaced with a golden tooth. He’s wearing a red turtleneck sweater with a black fur lined jacket and black basketball shorts with yellow strips down the sides.

“Tsk, guess ya saw right through me huh.”

Laughing, “nah, just felt it in ma bones.” The two of you burst out laughing as you continue to share stupid puns and jokes. Emma passes you your milkshake with a thumbs up, indicating that she made sure it was safe. Thanking her, you continue your conversation with Sans while Emma manages to gain the attention of a certain fire elemental.

You start really enjoying your conversation with Sans. Every time you exchanged jokes his eye lights would glow brighter and expand slightly. His voice was deep and husky, like it belongs on a late-night radio show. Honestly, it was a bit hypnotizing. You start throwing out cheesy pickup lines. Creating a flirting competition of sorts between the two of you. Earning fake gagging noise from Emma and multiple eye rolls from Grillby. 

“Oh my gosh! Emma! Tricks! They’re doing karaoke!” Sami yells, quickly stumbling her way over to you. “You should totally do it!”

“No.”

“Whyyyyyyy?” She whines as she drapes over you again.

“Because, I don’t feel like it.” Which is true, you really don’t feel like moving unless you have too. You much rather hang with Sans and drink your third milkshake.

“Oh, come oooo-” She squeaks as she gets hip checked into Emma’s lap.

A wild dick hunter appears.

A random, scantily clad women in high death heel pushed Sami out of the way in order to get closer to Sans. She’s wearing a bedazzled bra with a sheer shirt on top paired with a mini skirt. She reeks of booze and apparently Sans agrees if that nasal bone wrinkle is any indication.

“Oh Sansy~” She says in a singsong voice. “Are you going to be singing tonight?”

Before Sans can answer, “You sing?” You ask generally curious.

“Uh, who are you?” She asks with a glare, leaning on Sans for both support and seduction.

That look on Sans face. 

That’s the look of a man who just earned the loser trophy. 

And it takes everything in your power not to laugh.

“Ah are you even listening to me.” She asks snapping her fingers in your face.

Zoning back in you, Sans is looking at you with mild concern. “Oh sorry, I didn’t notice your existence.” You tell the woman. Your group bursts out laughing as you go back to idly drinking your milkshake.

Her face is red as she glares down at you. “Whatever bitch. Why don’t go back home. Isn’t it past your bedtime, grandma?” She says in a condescending tone, completely missing Sans’ glare.

“Oh. No. She. Didn’t.” Sami stands from her spot in Emma’s lap and moves in front of you. “You did NOT just call her a gramma.”

“Uh, yeah I did.”

“Bitch! No one calls her a gramma and gets away with it!”

Leaning back to whisper to Emma and Grillby, “Didn’t Aims call me gramma earlier?”

“Nah she called you gram, there’s a difference.” She states matter-o-factly.

Playfully swatting at her, the three of you quietly chuckle amongst yourselves; calming Sans down a bit, but not Sami.

“I bet she could kick your ass at karaoke!” Sami challenges.

“Oh please, I’d like to see you try bitch!”

“Fine, then we’ll see you at the stage!”

“Fine!”

“Fine!”

“Why?” You whine as she walks away.

“Cause I’m defending your honor.” Sami replies proudly.

“It’s not defending me, if I still gotta work.”

“Come on, please just do it.”

Thinking on it for a moment before sighing in resignation. “Fine, I’ll do it. Got the perfect song in mind anyway.” Finishing up your milkshake you get off your stool, gesturing for Emma to do the same. “Mind coming with, I need ya to hold my stuff while I’m on stage.” Emma shrugs but you know that’s a yes. Sami hops in place, cheering you on. Walking away, only to stop and face Sans, “You better be in the front row since this is all inadvertently your fault.” You point at Sans before heading over to the stage. Smirking he gives you a two-finger salute before disappearing.

It doesn’t take you long to pick out a song, you’re just happy they actually have it. Dragging Emma to the bathroom, you remove your hoodie dress to reveal your actual club dress.

“So, you did dress for the occasion.” Emma teases.

“Apparently so.” You say with mock surprise. Grinning you hand her your clothes. Now that you’re doing this, you’re going all out, and you can’t wait to troll this bar. A devil-ish grin graces your lips as you wait backstage. Emma left to watch from the bar with Sami and Grillby. Sans is in the front row, drinking a bottle of mustard. Gross. The party pooper is on stage trying to dance sexily while singing off key.

It isn’t long before her song is over and she blows a kiss in Sans direction. He shiver in disgust but she seems pleased with it. Walking off stage she shoulders checks you but only ends up stumbling as you firmly hold your ground.

The opening to the song starts as you slowly walk on stage. The spotlight hits you and in all seriousness you sing your chosen song while making eye contact with Sans.

_ When I first looked in your eyes. _

_ You were more than just a beauty to me. _

_ All my senses shot straight up. _

_ I was rock hard emotionally. _

You dance slowly. Elegantly. Moving your hips side to side and letting your body flow to the music. Using your hands to guide the audience’s eyes to specific parts of your body as you punctuate certain lyrics.

_ The fact that you and I could plow. _

_ Is something I haven’t even thought about. _

_ Starting now. _

You wink at Sans.

_ (wo-ao-aoh) _

_ I’ve got a heart boner for you. _

_ (wo-ao-aoh) _

_ I stand before you stiff and true. _

_ I wanna blast a load of feelings onto. _

_ (wo-ao-aoh) _

_ This heart boner’s for you. _

Singing beautifully with heartfelt emotion you continue to dance around the stage. Moving your body in a way that screams “take me now” but still managing to be tasteful. The bar is full of laughter, yet you have their undivided attention.

_ You’ve helped me grow into a man. _

_ My shallowness is a thing of the past. _

_ I want to slam you with my empathy. _

_ And then I’ll rail you with my class. _

You effortlessly reverse grind on stage. Making it look like someone is thrusting into you. Eyes full of lust and lips parted breathlessly as you stare at Sans. Gracefully moving to a crouch position, you slowly stand, dragging your hands along your body. Letting your clothes get caught on your fingers revealing bits of skin as you caress your own body.

_ You've helped me find maturity. _

_ I'll be your wiener king, tee hee. _

Hugging your shoulders, you give a bashful tee hee before spinning out.

_ (wo-ao-aoh) _

_ I've got a heart boner tonight. _

_ (wo-ao-aoh) _

_ Feel my love pants growing tight. _

_ I wanna plug you with respect all through the night. _

_ (wo-ao-aoh) _

_ I'll bust a nut of joy and light. _

Dancing and twirling around, you continue gesturing to Sans. Hands roaming your body in a seductive yet inviting way. Occasional revealing skin but always leaving a bit for the imagination. The audience is lit with a rainbow of color from the monster’s magic. Including a captivating red from Sans. Eye lights trained on you, watching every movement and gesture you make. His expression is of barely withheld lust as his grip tightens around the edge of the table. Even some of the human male audience are bent over with their hands in their lap.

Sliding down to the floor, shifting to be on all fours. You seductively crawl towards the front of the stage while panting.

_ H-h-h-h-heart boner. _

_ H-h-h-h-heart boner. _

_ Got a h-h-h-h-heart boner. _

_ H-h-h-h-heart boner. _

_ H-h-h-h-heart boner. _

Gesturing on the floor to Sans, mimicking being touched while you squirm, as though you’re having sex with another right in front of him. You hear a low growl and a crack coming from his direction.

_ You are the love that I pursue. _

_ Do you feel the feels I feel for you? _

_ There’s so much we have yet to do. _

_ Now jump me like a kangaroo! _

Suddenly, Sans appears on stage. Standing above you he snatches you from the floor and pulls you flush to his body. You’re shocked but you manage to continue singing, despite the minor hiccup.

_ (wo-ao-aoh) _

_ This heart boner’s for you. _

_ (wo-ao-aoh) _

_ I stand before you thick and true. _

_ I'll shoot a wad of gleaming romance just for you. _

_ (wo-ao-aoh) _

The two of you sing in harmony, teasing while seductively dancing around each other. Hands roaming, body brushing past each other, but your touch always remain tasteful. Hands never wondering to “restricted” areas. Spinning you out he quickly pulls you back against his chest.

_ Cause this heart boner’s for you. _

_ (wo-ao-aoh) _

Swaying together as the song comes to a close. Eye locked on one another you stop singing in favor of kissing the skeleton before.

Kissing you back with no hesitation you feel his grip tighten around you. The crowd cheers before it’s cut off by sudden silence. Opening your eyes, it’s dark and you aren’t in the club anymore. Sending Sans, a questioning glance, “my room.” He captures your lips in another kiss, melting into it when you kiss back. You’ll let this kidnapping slide for now.

_ It’s all for you. _

_ (wo-ao-aoh) _

_ Every throbbing inch of my heart is just for you. _

_ Screw you for judgin’ me… _

* * *

Notes:

This is either going to be a one-shot or it'll be two chapters. It depends on if I'm able to write so good smut. I hoped you guys enjoyed this chapter. This has been floating around in my head for a while now and I’m glad to finally get it out lol.

And yes Reader calls Ami, Aims it's not a type-o

[Tumblr](https://www.tumblr.com/blog/pumpkinflash)


	2. Velvet Seduction

**Summary for the Chapter:**

> Bedroom activities commence!

**Notes for the Chapter:**

> Okay so this is my first smut, sorry if it sucks but here you go! Sock fetish, biting, collar/leash play, spanking, and foot job. A lot of people give the skeletons sock fetishes but then do nothing with it, so I did.

Landing in his room, he traps you in a passionate kiss. Magic sparks against your lips sending bursts of heat straight to your core. A tongue runs across your lower lip causing you to gasp in surprise. He chuckles as he deepens the kiss. The vibration from his ribs rub against your erect nipples.

Your tongues rub and wrestle together enlisting moans and soft gasps from the two of you. Your hands trail up his body, feeling his ribs and the gaps between them. Separating, he quickly takes off his jacket. Taking the hint, you begin undressing yourself.

“keep the socks.” He growls out as he watches you remove your skirt.

“Whatever you say Red.” You tease, enjoying the red blush on his sweaty skull and the hypnotic red glow from his now exposed rib cage.

Quickly removing your heels, you spot a chain leash on his desk. Grabbing it you turn around just as he removed his short leaving him in his collar and red boxer. Deciding to be daring, you clip the leash to his collar. With a sharp tug you pull the shocked skeleton down to your level. Eyes sockets lidded and eyelights hazy, you pull him in for an intense kiss. Forcing all your love, lust, and desire into it. Cupping his jaw with your free hand, you lick his teeth asking for entrance.

Sharp teeth parting you carefully lick and explore the inside of his mouth. Running your tongue over his canines and the roof of his mouth. Paying close attention, to the areas that cause him to moan into the kiss. He’s panting hard as his knees gives out. Falling back onto the bed, holding you close to not break away from the kiss.

Watching him through lidded eyes, his sockets are closed as he lets himself get lost in the kiss. Allowing his tongue into your mouth you suck on it hard.

His eye sockets fly open as his body shudders and a long-broken groan escapes from his gasping maw. You can feel your pussy twitch at the sight. His sockets are lidded, eyelight flickering between spheres and inverted hearts while his soul glows a rich crimson red.

Leaning back, you tighten your grip on his leash as he follows you like a lovesick puppy. Lifting your foot up you gently run it over his exposed ribs. Receiving a shiver and purr in response, you continue. Rubbing your foot up and down his ribs. Letting your socked cover toes glade across them. Exploring each gap, crease, and crack.

With a shudder he shakily exhales, “d-damn sweetheart.” He groans out leaning into your touch. Enjoying the way your velvet socked cover feet run along his bones. The little nubs of your toes exploring each nook and cranny. Lightly gripping and flicking each bone causing him to shudder and rattle in pleasure. His hands come up to rub along your leg. Groping and kneading from your calf up to your thighs. Enjoying the way your socks squeeze your thighs and the small gap of exposed skin between your socks and panties.

A low growl leaves his rib cage when he notices just how wet you are. He wants to grab you by the straps of your garter belt and pull you to him. Wrap your warm thighs around his head as he plunges his tongue into your pussy.

He didn’t realize how close he got to your crotch until you used your foot to kick him back. Not expecting it, he fell until he was laying on his bed, feet still firmly planted on the floor. Walking between his legs, leash hanging limply in your hand.

“No need for daydreaming when I’m right here.” You tease with a smirk. Glancing down at his trap member your gaze drifts up to his face. His expression of nervous anticipation. “Now,” you drawl. Stepping on his chest, you use the leash as leverage and hoist yourself onto the bed. Standing over him, you press your heel into his sternum. “What do you want bone boy?” You ask in a seductive tone.

With a growl he grinds his hips into the air, wanting some form of friction. His blush spreads and deepens in color as he nervously looks away. “step on me.” He manages to say between pants. Pushing his embarrassment and pride to the side.

Eyeing him with a sadist smile you raise your foot only to slam it down on the bulge still trapped in his boxer. Gasping from the sudden pleasure and pain, his hips buck into your foot as his skull snaps backwards. Pressing down on your foot, rubbing and grinding his dick into his pelvis you watch as his body quacks and quivers in pleasure.

“f-fuck…more...h-harder…” He pants outs lifting his hips into your grinding foot. Deciding to mix it up you press down on your heel before shifting to a rocking motion. His moans increase as his hand fly over his head to grip at the messy sheets.

You didn’t think you had a sadistic streak in you but this. This is really working for you. Licking you lips you increase you pace, keeping your eyes on the skeleton beneath you. Rocking his hips in time with your rubs causes his dick to spring free. His dick is a vibrant crimson about average in length but quite girthy. Precum is already dripping down his shaft, coating his member in a red liquid and leaving your foot damp.

A whine escapes him as you stop your ministration. Bucking his hips in the air missing the pleasure filled pain already. His hazy eyelights follow your form as you move to sit down between his legs. A challenge in your eyes as you stare at his member. Licking your lips as you move both feet to either side of his dick. He can’t help but mimic your actions. Licking his sharp teeth, he spreads his legs wider to give you more room. He wiggles his hips as he impatiently waits for what is to cum.

Before he can beg you to continue, your feet are already on him, stroking up and down his shaft. Toes digging into the sides of his dick, feeling like little beads rolling across his dick. Gasping and twitching his hands instinctively reaches for your hips to find nothing. He wishes he could reach you, that you sat on his chest so he could sink his claws into your delicate skin but instead he settles for the sheets.

A breathy chuckle escapes your lips as you watch him flounder with his hands. Your legs and feet are getting tired, but you really want to see if you can make him cum from your feet alone. Shift between rubbing your foot on the tip to stroking the shaft you ignore the heat pooling in your lower belly. Bringing a hand up to grope your boob, pinching and twisting your nipple. The sensation of wanting to be touched, to be ravished, washes over you. Muffled moans escape you as you try to focus on getting him off instead.

A loud growl snaps you out of your focus as he grabs your hand holding the leash. In the blink of an eye he pulls you forward and flips you under him. Face down in the pillow you wonder if you messed up or read him wrong. Before you can look back a swift smack meets your cheeks, pulling a surprised yelp from your lips. A pleased purr escapes his rib cage as he kneads your ass before roughly smacking it once again.

“like that babygirl?” He teases, voice dangerously low.

“Mmm y-yes.” Again, you didn’t think you were into spanking, but the pain and pleasure send shockwave to your core. Making you lose your mind.

Another harsh smack makes your ass jiggle, much to his pleasure. Kneading your now red ass, “mmm red’s a good color fer ya.” He drawls out. Tearing away your soaked panties, you squeal as the cold air brushes against your wet folds. Lifting your hips, he spreads your cheeks to get a better view. Aligning his member with your entrance, “now it’s time fer some real fun.” He says before thrusting his member inside of your soaked pussy. A wave of pleasure shakes your form as you release a strangled cry.

Not being used to having something so thick inside you, you can’t help as you squeeze your vaginal walls around his hot throbbing member. Little moans and whimpers escape your lips as you wait to get used to him.

“babe, c-can...i”

Not letting him finish that sentence, “Yes!” You moan out causing him to start thrusting. “P-please. Please fuck me!” You scream, reaching your limit and wanting release. Begging for it as he pounds into you. His groans and moans only fueling your desires and bringing you closer to the edge.

Biting and nipping at your neck and shoulder he continues slamming into you at a breakneck pace. The feeling of your soft warm walls tightly squeeze against his dick is an addictive contrast from the pleasure filled pain of your sock covered feet grinding into his dick. Tongue lolling out of his mouth as he languidly runs it along your shoulder and the bite marks. He doesn’t think he’ll last and from how tight your pussy is getting, neither will you.

Thrusting in time with his, you’re almost there. “Please, j-just a…lil more.” You pant out. Eyes heavy lidded, mind blanking on everything but chasing your release.

Pinning you down to the bed Sans redouble his effort. Wishing that his collar was on your neck so he could pull your chain and force your neck back. Gripping your hair, he tugs on it bringing your head up and exposing your neck and shoulders. Staring at the light bite marks that litter the area it’s not enough. He needs more. He needs to make sure no one messes with you, that you know who you belong to.

He needs to mark you.

“**mine.**” He growls out before opening his maw wide and biting down on the nape of your neck. He pierces the skin, drawing blood and flooding your neck with his magic.

The pain from the bite is enough to send you over the edge. Back arching, you cum around his throbbing cock while screaming his name. Vision turning white as a sinful mixture of pain and pleasure fills your body. 

A couple more thrusts and he’s following you in his orgasm. Releasing hot streams of red cum into your awaiting pussy. Shoving his dick in as far as it will go, to ensure that his cum fills your womb. Releasing your nape, he enjoys the way your vagina continues to twitch and pulse around him. He gives you a few more thrust before pulling out and allowing his member to dissipate.

You gracefully slump into the bed missing the full sensation of having his dick inside you. Small whimpers leave your tired form at the feeling of cum leaking out of you. Closing your eyes, you feel Sans flop down next to you and bring you in close to his rib cage. Enjoying the warm sensation in your chest. You feel exhausted yet at peace. He strokes your messy hair, murmuring into your ear, “should go take a shower.”

Snuggling into his warm embrace, you mumble back, “Later.”

His soul pulses as he watches your sleepy form in his arms. Chuckling he kisses your forehead. “should really take care o’ ya first. ya can sleep later.” 

Refusing to open your eyes or move, you huff and snuggle deeper into the bed. “You do it.” You sass, voice tired and full of sleep.

“hhmmmm my pleasure.” He whispers into your hair before hoisting you up and carrying you to the bathroom.

* * *

[Tumblr](https://www.tumblr.com/blog/pumpkinflash)

[Twitter](https://twitter.com/buni_tea)

**Notes for the Chapter:**

> Thanks for reading! This is my first completed story!!! Hope you could actually make it to the end and that it wasn’t to cringy. Again, this is my first smut and I’m pretty happy with how this turned out. But if you have any critiques or constructive criticism please let me know. Other than that, thanks for reading, sorry this took almost a year commenting, and leaving kudos!
> 
> See ya in the next story!


End file.
